The changeover from gasoline vehicles to electric vehicles has been more important as an approach to global environmental issues. Accordingly, electric vehicles (EV), plug-in hybrid electric vehicles (PHEV), and hybrid electric vehicles (HEV) have been developing, each of which includes a power source embodied by an energy storage device such as a lithium ion secondary battery. Such an energy storage device typically includes an electrode body having positive and negative electrodes, an electrode terminal, and a current collector electrically connecting the electrode body and the electrode terminal.
There has been conventionally proposed an energy storage device including electrode bodies that are joined and retained to a current collector so as to be hung from the current collector (see JP-A-2013-077546, for example). In this energy storage device, a plurality of legs extending downward from the single current collector is joined to the plurality of electrode bodies, respectively, such that the electrode bodies are hung from the current collector and retained.
A current collector included in an energy storage device, like the one disclosed in JP-A-2013-077546, is typically manufactured by processing, such as bending, a metal plate member having a predetermined shape.
Specifically, the current collector is a member obtained through metalworking. It is thus necessary to prevent a crack, a fissure, and the like of the plate member during processing, such as bending, the plate member. For example, a bending line is provided at an end with a cut-away portion called an escape, for relief of stress concentration that causes a crack and the like.
Such provision of a cut-away portion at a bent position can cause a phenomenon deteriorating reliability of the current collector such as increase in electric resistance and deterioration in strength if the bent position has a portion of a smaller sectional area than those at adjacent positions.